Mechanism of cell protrusion formation in electrical field: the role of actin.

An intense alternating current electrical field that imposes membrane-applied force on the cell surface can induce formation of cell protrusions (Popov, S.V. and Margolis, L.B. (1988) J. Cell Sci. 90, 379-389). This technique has been used to investigate the role of actin in the cell protrusion formation. Platinum replicas of the cytoskeleton were prepared to characterize the organization of the cytoskeleton in external force-induced protrusions. Bundles of microfilaments were found in the processes. A specific inhibitor of actin polymerization, cytochalasin B, as well as inhibitors of ATP synthesis (sodium azide and carbonyl m-chlorophenylhydrazone) did not change the morphology of electrical field-generated protrusions, revealed by scanning electron microscopy. However, organization of the cytoskeleton inside the processes changed drastically using these inhibitors. The results of these experiments demonstrate that (i) Membrane-applied force is sufficient to produce native-like cell protrusions, even in conditions where activity of the cytoskeleton is inhibited; (ii) Actin microfilaments can be organized into bundles directly under the action of membrane-applied force. The significance of these observations to cell protrusion formation under normal physiological conditions is discussed.